Semiconductor device with protective material and method for encapsulating

ABSTRACT

A semiconductor device and method for encapsulating the semiconductor device are provided. The method includes: forming a plurality of wire bonds on a surface of the semiconductor device by bonding each of a plurality of copper wires onto corresponding ones of a plurality of aluminum pads; applying a protective material around the plurality of wire bonds, the protective material having a first pH; and encapsulating at least a portion of the semiconductor device and the protective material with an encapsulating material having a second pH, wherein the first pH of the protective material is for neutralizing the second pH of the encapsulating material around the plurality of wire bonds.

BACKGROUND

1. Field

This disclosure relates generally to semiconductor devices, and morespecifically, to protecting copper wire bonds in the semiconductordevice.

2. Related Art

As the price of gold has seen a sharp increase in value over the pastfew years, the cost of producing semiconductors with gold wire bonds hasincreased proportionally. Semiconductor designers are searching forlower cost materials in order to control costs while maintaining orimproving reliability of the semiconductor devices.

Copper is becoming a more popular choice as an interconnection materialin semiconductor packaging because the cost of copper is a fraction ofthe cost of gold. Copper also offers superior electrical and thermalconductivity, develops less intermetallic growth, has greaterreliability of the bond at elevated temperatures, and has highermechanical strength and stability.

Copper wire bonding has not been a popular choice because it is morestressful to a typical aluminum bond pad than gold wire bonding, and therisk of physical damage to aluminum bond pad is greater. This is due togreater hardness of copper versus gold and the need to use more severewire bonding parameters (e.g. higher force, higher power, highertemperature) for copper wire bonding due to the greater hardness ofcopper and the slower growth of intermetallic layers versusgold-aluminum intermetallic layers. From the 90 nanometer integratedcircuit technology node onward, the back end of line (BEOL) layer stackhas been comprised of low dielectric constant (low K) dielectric andcopper layers, with a tantalum nitride or tantalum barrier layer betweenthe dielectric and the copper. The bond pad damage risk with copper wirebonding has become more severe with each new IC technology nodeincorporating increasingly lower dielectric constant interlayerdielectrics (ILD), and copper interconnect. The progressively lowerstrength of these low K dielectrics and the relatively low adhesionstrength between materials comprising the ILD-copper stack are thecauses of the increased risk of damage during wire bonding.

The risk of pad damage is also a function of bond pad design features.Increasing the aluminum pad thickness is known to reduce the risk of paddamage, but this can also increase the lateral displacement of aluminum(“aluminum push-out”) during the bonding process, risking damage to thepassivation layer, or even shorting between very fine pitch bond pads.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure is illustrated by way of exampleand is not limited by the accompanying figures, in which like referencesindicate similar elements. Elements in the figures are illustrated forsimplicity and clarity and have not necessarily been drawn to scale.

FIG. 1 is a cross-sectional diagram of an embodiment of a semiconductordevice in accordance with the present disclosure.

FIG. 2 is a cross-sectional diagram of a conventional wire bond on asemiconductor device.

FIG. 3 is a top view of an embodiment of a semiconductor device inaccordance with the present disclosure.

FIG. 4 is a flow diagram of an embodiment of a method for protectingwire bonds during the manufacture of a semiconductor device.

DETAILED DESCRIPTION

Embodiments of semiconductor devices and fabrication methods disclosedherein use a protective material over copper wire bonding on aluminumpads. An intermetallic layer is formed when the copper wire is bonded tothe aluminum pad. The protective material has a pH that neutralizescontaminants in an encapsulating material that otherwise causescorrosion in the intermetallic layer.

Referring to FIG. 1, a cross-sectional diagram of an embodiment of asemiconductor device 100 in accordance with the present disclosure isshown including copper wire 102, encapsulating material 103, aluminumbond pad 104, passivation material 105, protective material 106, firstintermetallic layer 108, second intermetallic layer 110, tantalum layer112, copper layer 114, one or more vias 116, and interconnect lines 118.

During fabrication, the end of copper wire 102 is heated to a liquidstate forming a ball on the end of wire 102 and this end of wire 102 isapplied to aluminum pad 104 through an opening in passivation material105, via a bonding capillary (not shown) thereby forming a ball bond 120to the aluminum bond pad 104. It is typical to form only sporadic pointsof intermetallic growth, or no intermetallic growth in regions 124 atthe lower edges of ball bond 124 in the vicinity of first intermetalliclayer 108 since there can be large displacement of aluminum in this areaand the force and ultrasonic energy imparted to the ball bond 120 duringbond formation may be poor in region 124.

Passivation material 105 can be made of silicon nitride, silicon oxide,silicon oxynitride, or other suitable material. Copper ball bond 120adheres to the aluminum pad 104 due to the formation of intermetallicbond layer comprising intermetallic layers 108, 110 at the interface ofthe flattened copper ball 120 and the aluminum 104. Intermetallic bondlayer 108, 110 is typically a bi-layer, with the intermetallic phase 108in contact with the bottom of ball bond 120 commonly held to have thecomposition of Cu₉Al₄, and the composition of the intermetallic layer110 in contact with the aluminum pad 104 commonly held to be CuAl or amixture of CuAl and CuAl₂. The intermetallic bond layer 108, 110, andthe thickness and continuity of the intermetallic bond layer 108, 110across the interface between copper ball bond 120 and aluminum pad 104may vary depending upon the bonding parameters utilized and subsequentthermal processing of the semiconductor device 100. It is known that thestructures and compositions of intermetallic bond layer 108, 110 canshow further changes with even longer exposure to elevated temperaturesor under long term use conditions, especially under conditions where theentire thickness of aluminum pad 104 has been consumed with theformation of intermetallics. Under such conditions the intermetallicstratification may show three layers, or an even more complex structurethan shown for the purposes of illustration in FIG. 1. For purposes ofdescription of the present disclosure, the structure of intermetallicbond layer 108, 110 shown in FIG. 1 will be used. The chemicalcomposition of intermetallic layer 108 can be Cu₉Al₄, which is copperrich compared to intermetallic layer 110 which has a chemicalcomposition of CuAl, or a mixture of CuAl₂ and CuAl.

Tantalum layer 112 forms a barrier between aluminum bond pad 104 andcopper layer 114. Vias 116 couple copper layer 114 to interconnect lines118. Note that semiconductor device 100 can include several additionalcopper layers 114 and interconnect lines 118, as well as dielectriclayers, integrated circuits, and other suitable components.

Semiconductor device 100 can be any type of circuit where a copper wireis bonded to an aluminum pad including a memory device, a microprocessoror other type of microelectronic assembly having integrated circuitry, asingle transistor, and/or single diode devices. Copper wire 102 can beexposed on the exterior of semiconductor device 100 for connectingsemiconductor device 100 to buses, circuits, semiconductor packagesubstrates, semiconductor package lead frames, and/or othermicroelectronic assemblies. Semiconductor device 100 is shown having onecopper wire 102 and aluminum bond pad 104 providing an external contact,however semiconductor device 100 typically has many more than the oneshown. It is not unusual for such semiconductor devices to have hundredsof external contacts.

As integrated circuit transistor feature sizes decrease, demands forhigher numbers of contacts continue to increase, resulting in limitedamount of space for the contacts. This constantly forces finer wire bondpad pitches, smaller bond pads, and greater bond pad design complexity.The smaller bond pads drive the demand for reduced bond wire diameter,further increasing the difficulty of achieving highly reliable wirebonds due to the continuous reduction of the ball bond-to-die bond area.Reliability of copper wire bonds may also be threatened by corrosion ofthis reduced bond area.

Protective material 106 is deposited over ball bond 120 at the end ofcopper wire 102 and flows into an opening in passivation material 105 toenclose exposed portions of copper ball bond 120 and aluminum bond pad104, including the exposed portions, if present, of intermetallic layers108 and 110. Protective material 106 fully covers the periphery of ballbond 120 immediately adjacent to where ball bond 120 contacts aluminumpad 104 to prevent corrosion of intermetallic layer 108. Protectivematerial 106 may not fully cover the exposed surface of aluminum pad104, leaving regions 122 of aluminum pad 104 exposed, or protectivematerial 106 may fully cover the surface of aluminum pad 104 and alsocover the edge of the opening in passivation material 105.

Encapsulating material 103 is then deposited over semiconductor device100 including copper wire 102 and protective material 106. Protectivematerial 106 seals intermetallic bond layer 108, 110 from corrosivesubstances that may be present in encapsulating material 103.

In some embodiments, protective material 106 is dispensed as soon aspossible after copper wire 102 is bonded to aluminum bond pad 104 soheat from the bonding process can be used to help cure protectivematerial 106. For example, protective material 106 is applied tosemiconductor device 100 after semiconductor device 100 has been heatedto a temperature between 125 and 250 degrees Celsius and copper wire 102has been bonded to aluminum bond pad 104. Protective material 106 can befurther cured by applying thermal energy, microwave energy, infraredenergy or ultraviolet energy to semiconductor device 100. It is alsopossible that protective material 106 may initially contain a liquid orliquids that function as a solvent or carrier for the other constituentsof protective material 106. In this instance, curing may involve, inwhole, or in part, the evaporation of the liquid or liquids.

In some instances, the material selected for protective material 106establishes a pH that will neutralize the pH established inencapsulating material 103 in the presence of moisture. For example,protective material 106 can have a pH of greater than about 7.0 when theencapsulating material 103 has a pH of less than about 7.0.

Protective material 106 can comprise filler material 107 suspended in aliquid polymer system that may contain solvent or carrier liquids, whichafter curing would establish a neutral to mildly alkaline pH in a rangeof approximately 7-10 in the presence of moisture. Filler material 107can be a composition of, for example, magnesium hydroxide, aluminumhydroxide, calcium carbonate, magnesium carbonate, and/or calciumhydroxide, or other materials capable of establishing a neutral tomildly alkaline pH within the volume of the protective material 106 inthe presence of moisture. Filler material 107 can include particulateswith a diameter of between 0.005 to 30.0 microns (μm), and the types offillers used can have a surface area in a range of between 0.5 to 500.0square meters per gram (m2/g), with the high surface area materialscontaining a high fraction of very fine, or nano-size particles. Fillermaterial 107 can be in range of about 25 to 90 weight percent of theprotective material 106. Protective material 106 can have a thicknessranging between 0.005 millimeters (mm) and 0.250 mm, and morespecifically, in some embodiments, between 0.010 and 0.100 mm. Theliquid polymer can have a low viscosity to assure a desired level ofwetting and can have a viscosity in a range of between about 30.0 to6000.0 milli-Pascal seconds (mPa·s) when measured at shear ratestypically used in defining viscosity of dispensable filled liquidpolymer systems. Other suitable compositions of filler material 107 andviscosities of uncured protective material 106 can be used. The term“composition” as used herein includes chemical substances as well asfiner and coarser particle size distributions, higher and lower weightpercent fillers, and higher and lower specific surface areas.

Encapsulating material 103 is generally a plastic or epoxy compound thatcan be molded to form a casing over the die to seal the die from theexternal environment and shield the die from electrical and mechanicaldamage. Conventional techniques for encapsulating die include transfermolding, compression molding, and dispensable systems commonly referredto as glob top encapsulants.

FIG. 2 is a cross-sectional diagram of a conventional copper wire 102bonded to aluminum bond pad 104 in a semiconductor device 200 shown toillustrate the problems that may arise when encapsulating material 103is in contact with intermetallic bond layer 108, 110 shown in FIG. 1. InFIG. 2, encapsulating material 103 may contain various levels ofcontaminants. To varying degrees, depending upon type of polymer system,type of filler, ratio of filler to polymer system, degree of cure orcross-linking, polymeric encapsulating material 103 will be capable ofabsorbing and adsorbing water from the ambient environment. The watermay dissolve, or react with constituents of encapsulating material 103freeing species that form cationic and anionic contaminants in thewater. The anionic species, including, but not limited to, halogens,sulfur compounds, and organics can readily establish a pH of less than 7within the volume of encapsulant 103. If the encapsulating material 103contains a sufficiently high level of contaminants, the pH can becomequite acidic, with a pH of less than 5. Once the ionic species areformed in combination with the water, these ionic species become quitemobile and can readily diffuse through the encapsulant 103.Intermetallic bond layer 108, 110 (shown in FIG. 1) may be subjected tothe corrosive contaminants in an acidic environment if encapsulatingmaterial 103 contains contaminants above a certain level. The problem isexacerbated when voltage is applied to semiconductor device 200. Forexample, in order to pass a manufacturers reliability requirements,semiconductor device 200 may be subjected to biased Highly AcceleratedStress Testing (B-HAST) or other tests, such as aTemperature-Humidity-Bias test (THB). B-HAST typically applies higherthan nominal voltage to semiconductor device 100 in an ambientenvironment of 130° C. and 85% relative humidity for 96 hours or more.

In the acidic pH environment intermetallic bond layer 108, 110 iscorroded under the action of electrolyte contaminants, thought to beprincipally anions, including halogen ions. It has been observed thatthe corrosion occurs principally or exclusively in the copper-richintermetallic layer 108 in contact with the copper ball bond 120. Underother conditions, it may be possible to corrode an intermetallic layercomprised of less copper-rich intermetallic phases. The corrosionpenetrates under the copper ball bond 120 creating a void layer 204between copper ball bond 120 and an oxidized corrosion product layer 206on intermetallic layer 110. The copper rich intermetallic layer 108(shown in FIG. 1) is essentially consumed while the more aluminum richintermetallic layer 110 remains essentially intact. In FIG. 2 the volumepreviously occupied by intermetallic 108 (shown in FIG. 1) is replacedby a void layer gap 204 and an underlying corrosion product layer 206due to the corrosion of the original intermetallic layer 108 (shown inFIG. 1).

One option to prevent or reduce corrosion of intermetallic layers 108and/or 110 is to determine detailed chemical characteristics ofencapsulating material 103 that are less likely to cause corrosion andrequire suppliers to use materials and processes that will provide thespecified chemical characteristics with encapsulating material 103. Thisoption is likely to increase production costs if the supplier has tospecial order a small quantity of special constituents to makeencapsulating material 103, or to alter the percentage of normalconstituents of encapsulating material 103 in order to supply smallquantities of encapsulating material 103. This is because the suppliertypically uses a greater amount of different encapsulating materialconstituents to make the standard encapsulating material 103 at lowercost due to bulk pricing, and makes larger batches than would berequired for a customized version of encapsulating material 103.

As an alternative, protective material 106 protects intermetallic layers108 and 110 from corrosion and allows a broader selection of standardencapsulating material 103 to be used while lowering cost and level ofeffort for the manufacturer and the supplier.

FIG. 3 is a top view of a larger section of semiconductor device 100 inaccordance with the present disclosure showing a series of ball bonds120 bonded to aluminum bond pads 104 around the edges of semiconductordevice 100. It is understood that while FIG. 3 shows a single row ofpads 104, the pads 104 may be disposed at any location across thesurface of semiconductor device 100. FIG. 3 shows two options forapplying protective material 106. A first option is to dispenseprotective material 106 over each wire's ball bond region individually,as shown on the left edge of semiconductor device 100. A second optionis to dispense a continuous strip of protective material 106 along a rowof wire bonds to coat each wire's ball bond region, as shown along thelower edge of semiconductor device 100.

Generally protective material 106 can be dispensed using some form of aneedle dispenser. This type of dispenser may use a range of methodsinvolving various types of pumping mechanisms to dispense protectivematerial 106. These mechanisms include constant displacement andArchimedes screw pumps, and jet dispensers that typically use apiezoelectric actuator to dispense tiny, individual droplets of materialwith high frequency pulses. It is understood that other forms ofdispensing, or applying protective material 106, are anticipated. Therheology of protective material 106 may be tailored with modification ofthe filler material particle size distribution and specific surfacearea, and possible inclusion of a small quantity of a thixotrope, anextremely fine particle size and very high surface area material, tominimize the flow of dispensed protective material 106 after it isdispensed to assure the bulk of the material remains on the surface ofball bond 120, the region around the periphery of the ball bond at thesurface of the aluminum pad, and on some or all of the surface ofaluminum pad 104 that remains exposed outside the periphery of ball bond120.

FIG. 4 is a flow diagram of an embodiment of a method 400 for protectingwire bonds during the manufacture of a semiconductor device. Process 402includes bonding copper wire 102 to aluminum bond pad 104 using acombination of heat, pressure, and ultrasonic energy to make a weld orball bond. One or more intermetallic layers 108, 110 are formed duringthe bonding process.

Process 404 includes applying protective material 106 over ball bond120. The protective material 106 has a pH that neutralizes theacidifying effect of mobile contaminants found in the surroundingencapsulating material 103 in the presence of moisture, that may diffuseinto protective material 106, thus maintaining a neutral to mildlyalkaline pH in protective material 106. Maintenance of the neutral tomildly alkaline chemistry in protective material 106 prevents corrosionof intermetallic layer 108, 110, which would degrade or destroy the bondbetween copper wire 102 and aluminum bond pad 104, resulting in anincrease in resistance or an open circuit between the ball bond 120 andaluminum pad 104. To help decrease the amount of time required to cureprotective material 106, protective material 106 can be applied whilesemiconductor device 100, including copper wire 102, ball bond 120 andaluminum pad 104 are still hot from the bonding process. Accordingly,the dispensing of protective material 106 can be integrated into process402 to occur on a semiconductor device 100 immediately after wirebonding on semiconductor device 100 is finished and the wire bonding hadbegun on the next semiconductor device 100. Alternatively, protectivematerial 106 can be dispensed after semiconductor device 100 has beenheated to the desired temperature in the dispensing operation. As afurther alternative, protective material 106 can be dispensed onsemiconductor device 100 and cured in an oven at the appropriatetemperature. It is understood that a separate final cure operation, suchas an oven cure, or irradiation with microwave energy, infrared and/orultraviolet energy, may be required after the initial dispense process404 and cure process 406. It is also understood that cure process 410may also contribute to the final curing of protectant dispensed inprocess 404 while cure process 410 is effecting the cure of theencapsulant applied in process 408.

Dispensing protective material 106 onto a semiconductor device 100 thatretains the heat of the bonding operation or has been reheated to thedesired temperature may cause the dispensed protective material 106 toquickly begin to cure either by cross-linking or by evaporation ofsolvents and carriers. Beginning the cure immediately after dispensingprotective material 106 causes the viscosity to increase before flow ofthe dispensed protective material 106 away from desired locations canoccur. Protective material 106 may be formulated to partially or fullycure due to being dispensed onto the hot semiconductor device 100. Ifthe protective material 106 is formulated with liquid solvents andcarriers, essentially all of these materials can be volatilized beforethe semiconductor device 100 is encapsulated with encapsulation material103. In some embodiments, protective material 106 does not showsubstantial volatilization of constituents with evolution of gases(“off-gassing”) during the process of encapsulation with encapsulatingmaterial 103 or during a secondary curing operation, or post-mold cure,which is commonly required with use of a transfer molded thermosetepoxy-based encapsulant 103. If protective material 106 is onlypartially cured by the process of dispensing onto a heated semiconductordevice 100 and will not show substantial off-gassing in subsequentprocesses, then the semiconductor device 100 may be encapsulated withencapsulating material 103 as long as there are no undesirable chemicalreactions between partially cured protective material 106 andencapsulating material 103 during the process used to encapsulate withencapsulation material 106 or during a possible secondary cure, orpost-mold cure. Under these circumstances, both protective material 106and encapsulating material 103 will be fully cured simultaneously, whichcan enhance the bond between protective material 106 and encapsulatingmaterial 103.

Process 406 includes allowing the protective material 106 to cure on andabout the region of the ball bond 120 in desired locations at anappropriate temperature for an amount of time that allows the materialsto cure to the desired level. Process 406 may include irradiation withmicrowave energy, ultraviolet and/or infrared light. Process 408includes applying encapsulating material 103 over the desired portionsof semiconductor device 100. The pH established by the constituents andcontaminants in encapsulating material 103 that are likely to diffusewithin encapsulating material 103, and cause corrosion of intermetalliclayers 108,110 during extreme environmental testing and operatingconditions will be substantially neutralized by the pH of protectivematerial 106, thereby preventing or at least reducing corrosivesubstances from reaching the ball bonds.

The semiconductor device 100 described herein can be made using anysemiconductor material or combinations of materials, such as galliumarsenide, silicon germanium, silicon-on-insulator (SOI), silicon,monocrystalline silicon, the like, and combinations of the above.

By now it should be appreciated that there has been provided protectivematerial 106 to be applied to copper wire ball bonds 120 so as to coatthe external surface and the exposed edge of intermetallic layers 108,110. In some embodiments, protective material 106 is formulated to bealkaline (pH>7) to neutralize acidic extractants (pH<7) formed byencapsulating materials 103. Protection from the corrosive effects ofthe acidic extractants allows reliable use of copper wire bonds onaluminum bond pads. Protective material 106 further allows use of anyencapsulating materials 103 that meet other reliability requirements ofthe package, such as providing for no critical delamination, to be used.Additionally, the need to characterize candidate encapsulating materials103, specification of new encapsulating materials 103 for use withcopper wire bonded products, and the added cost of specially formulatedencapsulating materials 103 is eliminated.

In some embodiments, a method for encapsulating a semiconductor deviceis disclosed that includes forming a plurality of wire bonds on asurface of the semiconductor device by bonding each of a plurality ofcopper wires onto corresponding ones of a plurality of aluminum pads. Aprotective material with a first pH is applied around the plurality ofwire bonds. At least a portion of the semiconductor device and theprotective material is encapsulated with an encapsulating materialhaving a second pH. The first pH of the protective material neutralizesthe second pH of the encapsulating material around the plurality of wirebonds.

Other aspects of the method can include curing the protective materialafter the step of applying the protective material. The protectivematerial can be cured by applying thermal energy, microwave energy,ultraviolet radiation and/or infrared radiation to the semiconductordevice.

In further aspects of the method, applying the protective material caninclude applying the protective material to the semiconductor deviceafter the semiconductor device has been heated to a temperature between100 and 250 degrees Celsius.

In still further aspects of the method, applying the protective materialhaving the first pH further can comprise applying the protectivematerial having a pH of greater than about 7.0 to the ball bonds andimmediate surrounding areas of the bond pad, and encapsulating at leasta portion of the semiconductor device and the protective material withan encapsulating material having a pH of less than about 7.0.

In still further aspects of the method, applying the protective materialcan further comprise applying the protective material comprising asuspension comprising a liquid polymer having a filler material forproducing a neutral to alkaline pH in the protective material in thepresence of moisture.

In further aspects of the method, the filler material can comprise oneor more of magnesium hydroxide, aluminum hydroxide, calcium carbonate,magnesium carbonate, and calcium hydroxide.

In further aspects of the method, the filler material can compriseparticulates having a diameter of between 0.005 to 30.0 microns (μm),and a surface area of the coarsest to the finest particles in the fillerparticle size distribution in a range of between 0.5 to 500 squaremeters per gram (m2/g), such that the surface area of the filler formedfrom this range of coarse to very fine particles has a surface areabetween these two extremes.

In further aspects of the method, the liquid polymer can have aviscosity in a range of between about 30.0 to 6000.0 milli-Pascalseconds (mPa·s) when measured at shear rates typically used in definingviscosity of dispensable filled liquid polymer systems.

In further aspects of the method, the protective material can be formedaround a bond interface region between each of plurality of copper wiresand the corresponding ones of the plurality of aluminum pads.

In other embodiments, a method for encapsulating a semiconductor deviceis disclosed that includes forming a plurality of wire bonds on asurface of the semiconductor device by bonding each of a plurality ofcopper wires onto corresponding ones of a plurality of aluminum pads. Aprotective material is applied around an interface region between eachof the plurality of aluminum pads and the plurality of wire bonds. Theprotective material comprises a suspension comprising a liquid polymerhaving a filler material for producing a first pH of greater than about7.0. At least a portion of the semiconductor device and the protectivematerial is encapsulated with an encapsulating material having a secondpH of less than about 7.0 in the presence of moisture.

In further aspects of the method, the first pH of the protectivematerial can neutralize the second pH of the encapsulating materialaround the interface region between each of the plurality of aluminumpads and the plurality of wire bonds.

The method can further comprise curing the protective material usingthermal energy, microwave energy, ultraviolet and/or infrared radiationafter the step of applying the protective material.

In further aspects of the method, the filler material can comprise oneor more of magnesium hydroxide, aluminum hydroxide, calcium carbonate,calcium hydroxide, and magnesium carbonate.

In further aspects of the method, the filler material can compriseparticulates having a diameter of between 0.005 to 30.0 microns (μm),and a surface area in a range of between 0.5 to 500 square meters pergram (m2/g).

In further aspects of the method, the liquid polymer can have aviscosity in a range of between 30.0 to 6000.0 milli-Pascal seconds(mPa·s) when measured at shear rates typically used in definingviscosity of dispensable filled liquid polymer systems.

In still another embodiment, a semiconductor device includes a pluralityof aluminum bond pads on a surface of the semiconductor device; aplurality of copper wire bonds, a copper wire bond of the plurality ofcopper wire bonds formed on each of the plurality of aluminum pads; aprotective material formed around the plurality of copper wire bonds,the protective material having a first pH; and an encapsulating materialapplied over at least a portion of the semiconductor device and over theprotective material, the encapsulating material having a second pH. Thefirst pH of the protective material is for neutralizing the second pH ofthe encapsulating material around the plurality of wire bonds.

In further aspects of the semiconductor device, the protective materialcan comprise one or more of magnesium hydroxide, aluminum hydroxide,calcium carbonate, calcium hydroxide, and magnesium carbonate.

In still further aspects of the semiconductor device, the protectivematerial can comprise a suspension comprising a liquid polymer having afiller material for producing the first pH of greater than about 7.0,and wherein the second pH of the encapsulating material is less thanabout 7.0 in the presence of moisture.

In still further aspects of the semiconductor device, the fillermaterial can comprise particulates having a diameter of between 0.005 to30.0 microns (μm), and a surface area in a range of between 0.5 to 500square meters per gram (m2/g).

In still further aspects of the semiconductor device, the fillermaterial can be in range of about 10 to 90 weight percent of theprotective material.

Because the apparatus implementing the present disclosure is, for themost part, composed of electronic components and circuits known to thoseskilled in the art, circuit details will not be explained in any greaterextent than that considered necessary as illustrated above, for theunderstanding and appreciation of the underlying concepts of the presentdisclosure and in order not to obfuscate or distract from the teachingsof the present disclosure.

Moreover, the terms “front,” “back,” “top,” “bottom,” “over,” “under”and the like in the description and in the claims, if any, are used fordescriptive purposes and not necessarily for describing permanentrelative positions. It is understood that the terms so used areinterchangeable under appropriate circumstances such that theembodiments of the disclosure described herein are, for example, capableof operation in other orientations than those illustrated or otherwisedescribed herein.

Moreover, the pH of the protective material and the encapsulant isunderstood to mean the pH that would be formed within the volume of theprotective material or the encapsulant when these materials are in thepresence of water. It is further understood that the pH of such filledpolymer systems is typically measured by subjecting powdered samples ofthe cured polymer systems to an extraction process using water, elevatedtemperatures such as approximately 85° C., and pressure in a closedsystem, and then measuring the pH of the aqueous extractant and callingthis pH the pH of the filled polymer system.

Although the disclosure is described herein with reference to specificembodiments, various modifications and changes can be made withoutdeparting from the scope of the present disclosure as set forth in theclaims below. Accordingly, the specification and figures are to beregarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope of thepresent disclosure. Any benefits, advantages, or solutions to problemsthat are described herein with regard to specific embodiments are notintended to be construed as a critical, required, or essential featureor element of any or all the claims.

Furthermore, the terms “a” or “an,” as used herein, are defined as oneor more than one. Also, the use of introductory phrases such as “atleast one” and “one or more” in the claims should not be construed toimply that the introduction of another claim element by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim element to disclosures containing only one suchelement, even when the same claim includes the introductory phrases “oneor more” or “at least one” and indefinite articles such as “a” or “an.”The same holds true for the use of definite articles.

Unless stated otherwise, terms such as “first” and “second” are used toarbitrarily distinguish between the elements such terms describe. Thus,these terms are not necessarily intended to indicate temporal or otherprioritization of such elements.

1. A method for encapsulating a semiconductor device, the methodcomprising: forming a plurality of wire bonds on a surface of thesemiconductor device by bonding each of a plurality of copper wires ontocorresponding ones of a plurality of aluminum pads; applying aprotective material around the plurality of wire bonds, the protectivematerial having a first pH; and encapsulating at least a portion of thesemiconductor device and the protective material with an encapsulatingmaterial having a second pH, wherein the first pH of the protectivematerial is for neutralizing the second pH of the encapsulating materialaround the plurality of wire bonds.
 2. The method of claim 1 furthercomprising curing the protective material after the step of applying theprotective material.
 3. The method of claim 2, wherein curing theprotective material comprises applying at least one of the groupconsisting of: thermal energy, ultraviolet energy, and infrared energyto the semiconductor device.
 4. The method of claim 1, wherein applyingthe protective material further comprises applying the protectivematerial to the semiconductor device after the semiconductor device hasbeen heated to a temperature between 100 and 250 degrees Celsius.
 5. Themethod of claim 1, wherein applying the protective material having thefirst pH further comprises applying the protective material having a pHof greater than about 7.0, and encapsulating at least a portion of thesemiconductor device and the protective material with an encapsulatingmaterial having a pH of less than about 7.0.
 6. The method of claim 1,wherein applying the protective material further comprises applying theprotective material comprising a suspension comprising a liquid polymerhaving a filler material for producing a neutral to alkaline pH.
 7. Themethod of claim 6, wherein the filler material comprises one or more ofmagnesium hydroxide, aluminum hydroxide, calcium carbonate, magnesiumcarbonate, and calcium hydroxide.
 8. The method of claim 6, wherein thefiller material comprises particulates having a diameter of between0.005 to 30.0 microns (μm), and a surface area in a range of between 0.5to 500 square meters per gram (m²/g).
 9. The method of claim 6, whereinthe liquid polymer has a viscosity in a range of between 30.0 to 6000.0milli-Pascal seconds (mPa·s) when measured at shear rates typically usedin defining viscosity of dispensable filled liquid polymer systems. 10.The method of claim 1, wherein the protective material is formed arounda bond interface region between each of plurality of copper wires andthe corresponding ones of the plurality of aluminum pads.
 11. A methodfor encapsulating a semiconductor device, the method comprising: forminga plurality of wire bonds on a surface of the semiconductor device bybonding each of a plurality of copper wires onto corresponding ones of aplurality of aluminum pads; applying a protective material around aninterface region between each of the plurality of aluminum pads and theplurality of wire bonds, the protective material comprising a suspensioncomprising a liquid polymer having a filler material for producing afirst pH of greater than about 7.0; and encapsulating at least a portionof the semiconductor device and the protective material with anencapsulating material having a second pH of less than about 7.0,wherein the first pH of the protective material is for neutralizing thesecond pH of the encapsulating material around the interface regionbetween each of the plurality of aluminum pads and the plurality of wirebonds.
 12. The method of claim 11 further comprising curing theprotective material using at least one of the group consisting of:thermal energy, ultraviolet energy, and infrared energy after the stepof applying the protective material.
 13. The method of claim 11, whereinthe filler material comprises one or more of magnesium hydroxide,aluminum hydroxide, calcium carbonate, calcium hydroxide, and magnesiumcarbonate.
 14. The method of claim 11, wherein the filler materialcomprises particulates having a diameter of between 0.005 to 30.0microns (μm), and a surface area in a range of between 0.5 to 500 squaremeters per gram (m²/g).
 15. The method of claim 11, wherein the liquidpolymer has a viscosity in a range of between 30.0 to 6000.0milli-Pascal seconds (mPa·s) when measured at shear rates typically usedin defining viscosity of dispensable filled liquid polymer systems. 16.A semiconductor device comprising: a plurality of aluminum bond pads ona surface of the semiconductor device; a plurality of copper wire bonds,a copper wire bond of the plurality of copper wire bonds formed on eachof the plurality of aluminum pads; a protective material formed aroundthe plurality of copper wire bonds, the protective material having afirst pH; and an encapsulating material applied over at least a portionof the semiconductor device and over the protective material, theencapsulating material having a second pH, wherein the first pH of theprotective material is for neutralizing the second pH of theencapsulating material around the plurality of wire bonds.
 17. Thesemiconductor device of claim 16, wherein the protective materialcomprises one or more of magnesium hydroxide, aluminum hydroxide,calcium carbonate, calcium hydroxide, and magnesium carbonate.
 18. Thesemiconductor device of claim 16, wherein the protective materialcomprises a suspension comprising a liquid polymer having a fillermaterial for producing the first pH of greater than about 7.0, andwherein the second pH of the encapsulating material is less than about7.0.
 19. The semiconductor device of claim 16, wherein the fillermaterial comprises particulates having a diameter of between 0.005 to30.0 microns (μm), and a surface area in a range of between 0.5 to 500square meters per gram (m²/g).
 20. The semiconductor device of claim 16,wherein the filler material is in range of about 10 to 90 weight percentof the protective material and the protective material has a thicknessranging between 0.005 millimeters (mm) and 0.250 mm.